Aesthetic ceramic veneered restoration

ABSTRACT

The present invention relates to an aesthetic dental restoration having a layered structure, which dental restoration has the appearance of a natural tooth. In addition, the present invention relates to a method for preparing such dental restorations. Particularly, the invention is based on the control of interaction between opalescence and fluorescence.

The present invention relates to aesthetic ceramic veneered dentalrestorations and to a process and system for producing such restoration.More particularly, the present invention is based on a process for theproduction of an aesthetic porcelain veneered restoration on the basisof a new shade build-up, based on a functional separation between twooptical phenomena, opalescence and fluorescence.

Dental restorations have been prepared in the prior art which comprise asubstructure of a metal or ceramic material, upon which substructurelayers of porcelain are applied. Generally, the substructure is coveredby a layer of opaque material to effect that the substructure has not anadverse effect on the appearance of the restoration in the mouth. It isdescribed in, for instance, U.S. Pat. No. 5,453,290 that a metalsubstructure is covered with an opaque layer, and a dentin layer.Generally, nowadays, ceramic or metal alloy substructures are firstcovered by an opaque layer, followed by an opacious dentin layer, adentin layer and finally an incisal porcelain layer.

Especially the last decades, there is a tendency to prepare dentalrestorations which have an appearance that differs as little as possiblefrom the natural teeth of a person needing a dental restoration. It isalso one of the primary aims of the present invention to prepare adental restoration that will blend in naturally with the remainingdentition in the mouth of the individual needing said restoration. Thatis, a primary aim underlying the present invention is to provide dentalrestorations which have the appearance of a natural tooth.

With this aim in mind, in the prior art the dental technician hasincorporated in the various layers of a dental restoration, colouringagents with the aim to adapt the colour of the restoration to the colourof the teeth in the mouth of the individual for which the restoration isproduced. Moreover, the surfaces of the restorations were treated suchthat these gave the impression of natural teeth.

However, such traditional veneering ceramics have a blocky appearance,while the actual shade of the restoration comes from the materialitself.

More in particular, the skilled person appreciates that the appearanceof an artificial tooth is not only dependent on colour and surfaceproperties, but that also the transmission behaviour of light isimportant. It is known that homogeneous transparent masses of porcelainwith a smooth surface give a reflecting and clear appearance, while theaddition of reflecting particles to the porcelain mass or a roughsurface create a diffuse light scattering; the light transmission ishindered. Opalescence and fluorescence are also important features.

Dental technicians generally add sufficient amounts of fluorescentmaterial, and particularly yttriumoxide in the porcelain material, sothat a “black hole” appearance under certain lighting conditions isprevented. The fluorescent material, however, also has a slightlyopaquefying effect; it creates a somewhat cloudy effect which hindersthe transmission of light and which has a negative influence on thetranslucency of the restoration made. That is, light only partlypenetrates the veneering material and is diffusely distributed insidethe material, giving the restoration its “coloured tooth” appearance.

Opalescense is an optic phenomenon, caused by the so-calledTyndall-effect of light absorption by particle light scattering. Tointroduce the impression of opalescence, it has been proposed to addblue pigments. However, such blue pigments give under different lightconditions different effects.

Although the dental technician was confronted many times with the goalto produce a dental restoration that will blend in naturally with theremaining dentition, so far this goal has not been totally reached.Exactly copying the shade of the adjacent teeth is a painstakingtrial-and-error task and does not always lead to success because of theindividuality of teeth.

The present invention aims to solve, or at least to reduce the problemsencountered in the prior art. It is based on the control of opalescenceand fluorescence properties in the porcelain or ceramic material used inthe preparation of dental restorations.

Particularly, in a first aspect, the present invention relates to adental restoration comprising one or more opaque layers covered by oneor more other porcelain layers, the opaque layers being situated closerto the core than the other porcelain layers, wherein at least one of theopaque layers contains a fluorescent material, and wherein the one ormore other porcelain layers are predominantly transparent andopalescent. That is, the fluorescence required to provide a naturalappearance originates from the deeper laying layers, while the requiredopalescence originates from the layers closer to the surface of thedental restoration.

In a second aspect, the present invention relates to a method oflayering porcelain on a structure of metal or ceramic comprising thesteps of applying a first layer or first layers of an opaque linermaterial containing a fluorescent material and in a subsequent stepapplying one or more layers of a translucent, opalescent material.

U.S. Pat. No. 4,741,699 describes dental porcelain before opalescensewas introduced. In this document is it aimed to match not only thecolour but also the fluorescence of teeth in restorations to that ofnatural teeth. Thereto, it requires that the inorganic pigment thatcauses the fluorescent effect is lower in the outer, more translucentlayers, because of light absorbance by the stained porcelain. It is wellknown that to obtain the same fluorescent effect in porcelain it isnecessary to increase the fluorescence, when other pigments areincreased because of light absorption effects. The present invention, onthe contrary, aims for a maximum opalescent effect, instead of uniformUV fluorescense. However, a minimum, but sufficient, amount offluorescent effect is still obtained in the restoration of the presentinvention.

In accordance with the present invention, it was surprisingly found thatthe transparent outer layer is responsible for a deeper penetration oflight to the fluorescent opaque layer where the light reflects backthrough the more translucent outer layer. This interaction gives alively, natural effect, which makes the acceptance or appearance of therestoration less dependent on the obtaining of an exact copy of theshade of the adjacent teeth, as is the case with traditional veneeringmaterials.

The fluorescent material creates a glow from deep within; the more lightenters the artificial tooth, the stronger the reflection and clarity ofsaid tooth. The opaque layer required by the present invention hencebreaks light, reflects it and gives fluorescence. The fluorescentmaterials used are excited by UV light and send out VIS light. The lightreflected and sent out by the lower opaque layer or layers amplifies theopalescence in the transparent upper layers.

By the present invention and particularly by the interaction betweenopalescence and fluorescence, it becomes possible to control the colourand light effects in the mouth.

The present invention will be further explained with reference to thedrawings in FIG. 1, wherein the principle of the invention isillustrated for a preferred embodiment.

Particularly, FIG. 1 shows at the left-hand side a standard layeredrestoration known from the prior art (traditional method), and at theright-hand side a preferred embodiment of the invention. In thetraditional method most of the light that falls on the restoration isdiffusely dispersed into the ceramic. In the method according to thepresent invention, the light is transferred much deeper into the moretransparent opalescent layers, and especially the more transparent andopalescent incisal, dentin and opaque/dentin layers and is for a greatpart reflected against the strongly fluorescent opaque layer and on thestrongly fluorescent modifier, which is present between the dentin andopaque/dentin layer, in such a way that it exits the ceramic, to give avery “lively” and natural appearance.

That is, the present invention involves a specific layering of porcelainon a structure of metal or ceramic to obtain a more naturally lookingopalescent and fluorescent effect by functionally separating opalescenceand fluorescence in that the opaque layer and, if present, a modifierlayer have relatively strong fluorescence and the outer transparentlayers give a strong opalescense, and have little fluorescence. Itappears that when the veneering material was build-up in such a way amuch more acceptable blending-in process with the rest of the dentitionis experienced. The reflected light from a strongly fluorescentmodifier, when present, and opaque layer interacts with the shade of thedentin layer, giving this effect.

In order to provide a sufficiently strong fluorescence, the opaque layerthat contains the fluorescent material should contain said fluorescentmaterial in a considerable amount. Preferably, the fluorescent materialis present in an amount of at least 2 wt. %, preferably in an amountbetween 2 and 5 wt. %, drawn to the weight of the porcelain materialwherein it is incorporated, such as in the opaque liner material.

Because opalescence is an optic phenomenon, caused by the Tyndall-effectof light absorption by particle light scattering, it is only effectivein optically transparent materials. Therefore the opaquefying effect byaddition of a fluorescent must possibly be avoided. Hence, the layers oftranslucent, opalescent material should in principle not containfluorescent material. However, the effects of the invention are stillobtained if the amount of fluorescent material in the transparent,opalescent layers is lower than 0.1 wt. %, drawn to the weight of thelayers forming said translucent material. Preferably, these layerscontain less than 0.05 wt. % fluorescent material

The fluorescent material used can in principle be any material that iscompatible with the opaque porcelain material and that is able to sendout visible light. In a preferred embodiment, the fluorescent materialcomprises and preferably consists of yttriumoxide.

The translucent, opalescent material should preferably have atranslucency of more than 30%. In a preferred embodiment thetranslucent, opalescent material is made of porcelain containing atleast 10% of an opal glass frit. Particularly good results are obtainedwith transparent porcelain layers which consist of 10-100 wt.-% opalglass frit with the following composition in wt.-% drawn to the weightof the total composition: 45-70% SiO₂, 0-20% Al₂O₃, 0-20% K₂O, 0-15%Na₂O, 0-5% CaO, 0-3% MgO, 0-4% CeO₂, 0-4% Tb₂O₃, 1-10% P₂O₅, 0-1% CaF₂,0-2% Li₂O, and 0-5% Sb₂O₃. Alternatively, equally good results areobtained with transparent porcelain layers which consist of 10-100 wt.-%opal glass frit with the following composition in wt.-%: 45-70% SiO₂,0-20% Al₂O₃, 0-20% K₂O, 0-15% Na₂O, 0-5% CaO, 0-3% MgO, 0-4% CeO₂, 0-4%Tb₂O₃, 0-2% P₂O₅, 5-15% CaF₂, 0-2% Li₂O, and 0-5% Sb₂O₃.

The dental restoration of the present invention comprises at least oneopaque layer that contains fluorescent material, and more to the surfaceof the dental restoration other porcelain layers which are translucentand opalescent. These other porcelain layers comprise at least oneincisal layer, at least one dentin layer, and optionally at least oneopaque/dentin layer. See in this respect, FIG. 1.

In a particularly preferred embodiment, the dental restoration of theinvention has a modifier containing fluorescent material present in anarea between the incisal layer or layers and the dentin layer or layersand/or between the dentin layer(s) and the opaque/dentin layer(s). Thismodifier makes it possible to provide an even better adapted naturallooking tooth.

Suitably, the modifier layer contains at least 0.1 wt. % yttriumoxide asfluorescent applied between the dentin and the incisal layer.

In accordance with this aspect of the present invention, when atransparent outer layer is used and when an internal highly fluorescentmaterial is used in-between the incisal and dentin layer, the process ofblending-in with the remaining dentition takes place easily, even if theshade is not exactly copied. The shade of the modifier layer interactswith the basic dentin material to give a play of light and shades, whichcan also be seen when teeth are observed under different lightconditions (morning, noon or evening; spring, summer, autumn or winter).

In the porcelains used to be applied to a substructure of either ceramicor a metal or metal alloy, colouring agents can be incorporated underthe precondition that these do not interfere with the interactionbetween opalescence and fluorescence.

In the method of the present invention, the preferred opal glass fritcontaining composition for the translucent layers to be applied,preferably have a firing temperature that is not lower than 25° C. thanthe firing temperature of the basic veneering material on which it isapplied. This should secure that the two materials do not react witheach other.

Finally, the present invention foresees in an easy-to-use ceramic systembuild-up for use in the method of the present invention. Thiseasy-to-use system ensures that the dental technician achieves thebenefits and advantages mentioned for the invention without exactlyneeding to know all the specific effects of each separate layer. Thissystem is embodied in TABLE A and is based on the colour indicationsused by the dental technicians (A1-D4). In this TABLE A, the action identin refers to the colour of the modifier layer used in the preferredembodiment of the invention, and the x-tra-incisals refer to the highopalescent layers according to the invention.

The present invention will now be further illustrated by means of thefollowing non-limiting examples. In these examples describing the methodand products of the present invention the following basis ceramiccompositions were used. The first ceramic composition used is veneeringporcelain C as described in U.S. Pat. No. 5,453,290. This product issold under the tradename “Carrara” (registered tradename of ElephantDental B.V., Hoorn, The Netherlands). The second ceramic material usedis veneering porcelain A used for standard ceramic alloys and is soldunder the name “Antagon” (registered trade name Elephant Dental B.V.,Hoorn, The Netherlands). Another basis veneering material S is soldunder the name “Sintagon” (registered trade name Elephant Dental B.V.,Hoorn, The Netherlands) and is used for the veneering of Y-PTZ zirconiastructures. In table 1, the composition of the three basic veneeringmaterials is given. TABLE 1 Composition in wt.-% of three basicveneering materials Component Material C Material A Material S SiO₂ 65.164.1 67.0 Al₂O₃ 12.5 14.2 11.0 K₂O 11.6 11.1 10.1 Na₂O 7.2 6.6 8.6 CaO0.7 1.1 0.8 BaO 0.9 0.4 1.3 Sb₂O₃ 1.5 1.4 2.1 Li₂O 0.3 0.2 0.2 F₂ 0.60.6 0.0 Translucency (%) 520 nm 1x 68.0 73.0 80.0 Translucency (%) 520nm 5x 65.0 70.0 80.0 Firing temperature, ° C. 860 900 830 Glasstransition temperature, ° C. 460 460 480 TEC μm/m.K (25 to 400° C.) 13.712.4 9.4 TEC μm/m.K (25 to 500° C.) 14.7 12.7 9.7

The translucency values in the present application are determined usinglight of a wavelength of 520 nm that passes through a disk of materialwith a thickness of 2.20-2.30 mm. The references “1×” and “5×” inrespect of the translucencies refer to the number of firing steps,required to apply the materials. The TEC is the thermal extensioncoefficient, which is determined either in the temperature range of25-400° C. or in the range of 25-500° C. as described in U.S. Pat. No.5,453,290.

EXAMPLES 1 AND 2

To obtain an opalescent effect, basic veneering materials A, C and S areblended with an opal glass frit (vide infra) in a proportion of 20 to 40weight percent. The translucency of the basic veneering materials isinversely related to the expansion of the frit, which is caused by thepresence of a crystalline leucite phase. Basic material A containsapproximately 22 vol. % leucite and basic material C about 30 vol.-%leucite, while composition S is leucite-free.

Two different opal glass frits were produced by blending severalmixtures of powdered metal oxides, carbonates or nitrates in theappropriate proportions. The blended powders were fused to form a glassmelt followed by quenching, drying, ball milling and seeving using meansknown in the art (Table 2). The powders formed from either one of thesetwo glasses having a particle size of less than 106 μm are pigmented toobtain a toothlike appearance. TABLE 2 Composition in wt.-% of twoopalescent glass frits. Component Ex. 1 Ex. 2 SiO₂ 62.0 62.6 Al₂O₃ 10.811.2 K₂O 9.6 7.6 Na₂O 7.4 7.6 CaO 3.3 0.1 MgO 2.0 0.0 CeO₂ 1.8 0.0 Tb₂O₃1.9 2.3 P₂O₅ 2.0 0.0 CaF₂ 0.0 9.9 Translucency (%) 520 nm 1x 57.8 66.3Translucency (%) 520 nm 5x 49.3 56.3 Opalescence 1x 17.5 24.7Opalescence 5x 20.8 24.7 Firing temperature, ° C. 900 835 Glasstransition temperature, ° C. 590 525 TEC μm/m.K (25 to 400° C.) 8.5 9.7TEC μm/m.K (25 to 500° C.) 8.8 9.3

The opalescence is measured as the calculated difference (ΔC) betweenthe a*- and b*-values according to the CIELAB colour space, whereby thesample is measured against a white and against a black background usingan artificial D65 light source. Particularly, the opalescence iscalculated as the square root of [(a*)²+(b*)²].

The opalescence found for example 1 is based on the crystallisation of afine phosphate phase, while in example 2 calcium fluoride crystals withan average size of 300 nm are generating the opalescence.

Both opalescent glass frits had the same or a better opalescence afterthey were fired 5 times at their firing temperature. However, theirtranslucency suffers from the light absorption caused by the increase incrystalline phase volume.

COMPARATIVE EXAMPLE 3

In the present example, dental restorations prepared according to thetraditional method and using the method of the present invention withthe materials described in examples 1 and 2 are compared. The resultsare depicted in Table 3. TABLE 3 Composition of ceramic C oftransparent, incisal, modifier, and opaque ceramic with opal fritExample 1 and Example 2 Component Transparent Incisal Modifier OpaqueTraditional Wt.-% Y₂O₃ 0.05 0.05 0.05 0.0 Translucency (%) 520 nm 1 60.025.0 25.0 0.0 Translucency (%) 520 nm 5 60.0 25.0 25.0 0.0 Fluorescence8 8 4 0.0 Opalescence 1x 0 10.0 0 N.A. Opalescence 5x 0 10.0 0 N.A.Method of Wt.-% Y₂O₃ 0.03 0.05 0.4 3.0 invention Translucency (%) 520 nm1 60.0 40.0 25.0 0.0 (Ex. 1 opal Translucency (%) 520 nm 5 58.0 40.025.0 0.0 frit, 29%) Fluorescence 2 4 10 Opalescence 1x 10.4 8.0 0 N.A.Opalescence 5x 12.7 8.0 0 N.A. Method of Wt.-% Y₂O₃ 0.03 0.05 0.4 3.0invention Translucency (%) 520 nm 1 62.4 40.0 25.0 0.0 (Ex. 2 opalTranslucency (%) 520 nm 5 60.7 40.0 25.0 0.0 frit, 29%) Fluorescense 2 410 Opalescense 1x 11.7 8.0 0 N.A. Opalescense 5x 8.1 6.0 0 N.A.

The degree of fluorescence is determined using a fluorescence indicatorwhich was specially adjusted for this purpose. The indicator contains 10discs numbered from 1 to 10 whereby disc 1 has the lowest concentrationof fluorescent and disc 10 the highest concentration of fluorescentmaterial.

Opal glass frit ex. 1 gave an increase in opalescence after 5 firings.

The firing temperature of basic veneering material C is 860° C. and thisis 40° C. lower than the firing temperature of ex. 1. The likelyhoodthat ex. 1 will react with the basic veneering material C is thereforesmall.

Opal glass frit ex. 2 gave a decrease after repeated firings because thefiring temperature is 25° C. lower than the basic veneering material C.

For both opal frits the translucency decreases after 5 firings due to adecrease of translucency in the basic veneering material.

COMPARATIVE EXAMPLE 4

In the present example, dental restorations prepared according to thetraditional method and using the method of the present invention withthe materials described in examples 1 and 2 are compared. The resultsare depicted in Table 4. TABLE 4 Composition of ceramic A oftransparent, incisal, modifier, and opaque ceramic with opal frit exp.1and exp. 2 Component Transparent Incisal Modifier Opaque TraditionalWt.-% Y₂O₃ 0.05 0.05 0.05 0.0 Translucency (%) 520 nm 1 50.0 25.0 25.00.0 Translucency (%) 520 nm 5 50.0 25.0 25.0 0.0 Fluorescence 8 8 4 0.0Opalescence 1x 0 10.0 0 N.A. Opalescence 5x 0 10.0 0 N.A. Method of theWt.-% Y₂O₃ 0.03 0.05 0.4 3.0 invention Translucency (%) 520 nm 1 70.240.0 25.0 0.0 (Ex. 1 opal Translucency (%) 520 nm 5 66.3 40.0 25.0 0.0frit, 29%) Fluorescence 2 4 10 Opalescence 1x 10.7 8.0 0 N.A.Opalescence 5x 14.3 8.0 0 N.A. Method of the Wt.-% Y₂O₃ 0.03 0.05 0.43.0 invention Translucency (%) 520 nm 1 65.3 40.0 25.0 0.0 (Ex. 2 opalTranslucency (%) 520 nm 5 67.0 40.0 25.0 0.0 frit, 29%) Fluorescence 2 410 Opalescence 1x 11.0 8.0 0 N.A. Opalescence 5x 7.7 6.0 0 N.A.

Opal glass frit ex. 1 gave an increase in opalescence after 5 firings.The firing temperature of basic veneering material C is 900° C. and thisthe same as the wring temperature of ex 1. The likelyhood that ex 1 willreact with the basic veneering material A is therefore small.

Opal glass frit ex. 2 gave a strong decrease after repeated firingsbecause the firing temperature is 65° C. lower than the basic veneeringmaterial A.

COMPARATIVE EXAMPLE 5

In the present example, dental restorations prepared according to thetraditional method and using the method of the present invention withthe materials described in examples 1 and 2 are compared. The resultsare depicted in Table 5. TABLE 5 Composition of ceramic S oftransparent, incisal, modifier, and opaque ceramic with opalfrit exp.1and exp. 2 Component Transparent Incisal Modifier Opaque TraditionalWt.-% Y₂O₃ 0.05 0.05 0.05 0.0 Translucency (%) 520 nm 1 80.0 25.0 25.00.0 Translucency (%) 520 nm 5 80.0 25.0 25.0 0.0 Fluorescence 8 8 4 0.0Opalescence 1x 0 10 0 N.A. Opalescence 5x 0 10 0 N.A. New method Wt.-%Y₂O₃ 0.03 0.05 0.4 3.0 (Ex. 1 opalfrit, Translucency (%) 520 nm 1 72.040.0 25.0 0.0 29%) Translucency (%) 520 nm 5 70.0 40.0 25.0 0.0Fluorescence 2 4 10 Opalescence 1x 10.4 9.0 0 N.A. Opalescence 5x 12.710.0 0 N.A. New method Wt.-% Y₂O₃ 0.03 0.05 0.4 3.0 (Ex. 2 Translucency(%) 520 nm 1 68.0 40.0 25.0 0.0 opalfrit, 29%) Translucency (%) 520 nm 566.0 40.0 25.0 0.0 Fluorescence 2 4 10 Opalescence 1x 11.7 8.7 0 N.A.Opalescence 5x 12.8 9.7 0 N.A.

Both opal glass frits ex. 1 and ex. 2 gave an increase in opalescenseafter 5 firings. The firing temperature of basic veneering material S is830° C., which for ex. 1 is 70° C. and for ex. 2 30° C. lower than thefiring temperature basic veneering material S. The likelyhood that ex 1and ex. 2 will react with the basic veneering material S is thereforesmall.

1. Dental restoration comprising one or more opaque layers covered byone or more other porcelain layers, the opaque layers being situatedcloser to the core than the other porcelain layers, wherein at least oneof the opaque layers contains a fluorescent material, and wherein theone or more other porcelain layers are predominantly transparent andopalescent.
 2. The dental restoration of claim 1, wherein the otherporcelain layers comprise at least one incisal layer, at least onedentin layer, and optionally at least one opaque/dentin layer.
 3. Thedental restoration of claim 2, wherein between the incisal layer and thedentin layer and/or between the dentin layer and the opaque/dentin layera modifier containing fluorescent material is present.
 4. Method oflayering porcelain on a structure of metal or ceramic comprising thesteps of applying a first layer or first layers of an opaque linermaterial containing a fluorescent material and in a subsequent stepapplying one or more layers of a translucent, opalescent material. 5.The method of claim 4, wherein at least 2 wt. % of a fluorescentmaterial is present in the liner material, drawn to the total weight ofthe liner material.
 6. The method of claim 5, wherein the fluorescentmaterial comprises and preferably consists of yttriumoxide.
 7. Themethod of claim 4, wherein the translucent, opalescent material containsless than 0.05 wt. % fluorescent material.
 8. The method of claim 4,wherein at least 10% of an opal glass frit is used as the translucent,opalescent material.
 9. The method of claim 4, wherein the translucent,opalescent material has a translucency of more than 30%.
 10. The methodof claim 4, wherein transparent porcelain layers are applied whichconsist of 10-100 wt. % opal glass frit with the following compositionin wt. %: 45-70% SiO₂, 0-20% Al₂O₃, 0-20% K₂0, 0-15% Na₂O, 0-5% CaO,0-3% MgO, 0-4% CeO₂, 0-4% Tb₂O₃, 1-10% P₂O₅, 0-1% CaF₂, 0-2% Li₂O, and0-5% Sb₂O₃.
 11. The method of claim 4, wherein transparent porcelainlayers are applied which consist of 10-100 wt. % opal glass frit withthe following composition in wt. %: 45-70% SiO₂, 0-20% Al₂O₃, 0-20% K₂O,0-15% Na₂O, 0-5% CaO, 0-3% MgO, 0-4% CeO₂, 0-4% Tb₂O₃, 0-2% P₂O₅, 5-15%CaF₂, 0-2% Li₂O, and 0-5% Sb₂O₃.